Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $230.92   13.788%   $262.7592   $262.76   $262.75   $262.80  
  Purchase #2 $85.74   10.855%   $95.0471   $95.05   $95.05   $95.00  
  Purchase #3 $9.41   6.326%   $10.0053   $10.01   $10.00   $10.00  
  Purchase #4 $233.93   13.776%   $266.1562   $266.16   $266.15   $266.20  
  Purchase #5 $98.99   9.364%   $108.2594   $108.26   $108.25   $108.30  
  Purchase #6 $126.36   4.278%   $131.7657   $131.77   $131.75   $131.80  
  Purchase #7 $46.74   12.119%   $52.4044   $52.40   $52.40   $52.40  
  7 purchase totals = $832.09       $926.3973   $926.41   $926.35   $926.50